so.. who can tell me anything about my double 400?

RooX · « **on:** 2 Jan 2004, 11:50 pm »

just got a "double 400" by V.A. for the princly sum of 300 canadian. Anyone care to tell me something about this beast of an amp? It is in PERFECT condition, the only problem being the on/off/fan switch which will not turn off (i can use the fan, and its constantly turned on) not a problem as its hooked into a conditioner with outlets that can be switched. So far the sound is quiet nice! I havent used a SS amp in years and its kinda fun.. Perhaps mabey not enough juice for my acoustats (seems a little quiet still, but i dont have a pre amp hooked up to it)

any info on it would be appreciated!

cheers,
Colin

spectralman · « **Reply #1 on:** 4 Jan 2004, 03:35 am »

Hi Colin,

If this is what I think it is, It's a Double Dyna 400. I used to own of of these back around 1980. It started life as a Dynaco Stereo 400 power amp. Frank doubled the number of output devices from 4 to 8 per channel, thus making it stable into a 2 ohm load. He also replaced a number of parts on the driver boards. If I remeber correctly, output is approx. as follows:

200-240W/ch into 8 ohms
380-400W/ch into 4 ohms
500W/ch into 2 ohms.

It should have an external capacitance box that connects on the lower right side of the chassis, giving it 100K MFD total of filter cap. All front panel controls should also be defeatable by an added-on bypass push button switch on the left front of the face plate.

In its day, it was a very highly rated SS amp. Its forte was driving cone or Magneplanar type speakers. I heard mine on Acoustat's and (at very low levels) on Quad ESL's. This amp did not like driving electrostatics at all, was very thin sounding.

How this amp fares in today's audio world I don't know, as I sold mine many many years ago. HTH.

RooX · « **Reply #2 on:** 4 Jan 2004, 04:33 am »

ah ha!
your right on the money.

i was wondering what the little plug on the lower right hand side was for (mine didnt come with the box) a friend of mine got a great shock putting a screwdriver on it while it was on! (no damage seems to have been done, to him or the amp

) Wonder where i might find one of those boxes!

on an aside. Now that i have left it on for most of the day, it is starting to sound pretty good with the acoustats. Certainly acceptable, perhaps a bit warm even???

cheers

spectralman · « **Reply #3 on:** 4 Jan 2004, 07:14 am »

You can actually make your own cap. box. Find some decent can caps of the correct voltage (check the ones in the amp already, at least 70 if I remember correctly). Frank connected them together in the box with aluminum? bar stock; you could also just wire them tohether. The hang-up will be finding the appropriate mating connector for what's already in the amp. Maybe Frank could help you with that. You will find with the added capacitance that the amp relay takes MUCH longer to click off.

avahifi_lj · « **Reply #4 on:** 5 Jan 2004, 08:20 pm »

Hi:

The Double 400 is from the mid-1970s. The amp uses bi-polar output transistors rather than the MOS-Fet devices used today. As the previous poster stated, the amp also had an external power supply box that increased the filtering in the power supply. You don't, however, need to have the outboard box to run the amplifier. The extra filtering was added to help stiffen the power supply.

If you don't have the external power supply box I HIGHLY recommend that you cover the jack with black electrical tape to prevent others from sticking things into the jack!

The power switch on the Dyna 400 series amps are known to fail. Sometimes you can take them apart and rework them, but I have not had too much success with them. When we offered upgrades to the Dyna 400 series we added a current limiter to the switch to help prolong the life, but if yours is already bad that won't help.

Treat the amplifier with care as they are no longer serviceable. The age of the parts may be approaching the end of their service life. Also note that it's likely very hard to find replacements for some of the parts.

An interesting note regarding the Double 400:
After Frank introduced the AVA Double 400 Dynaco borrowed the amp from one of our customers and liked it so much they copied the design and called it the Dynaco 416. If you look at the schematic of the AVA Double 400 and the Dynaco 416 you would see that the Dynaco 416 audio circuits are a part-for-part copy of the AVA Double 400....

Larry

RooX · « **Reply #5 on:** 6 Jan 2004, 04:18 am »

so are there any schematics for this fabled extra capitance box? black tape works.. but i would rather have a mammoth power supply

avahifi_lj · « **Reply #6 on:** 6 Jan 2004, 03:31 pm »

Hi:

I checked with Frank and he does not have a the schematic any longer; however, the box contained six 10,000uF 75V capacitors broken into two banks of three. One set of three is used for the positive rails and the second set for the negative rails. The amp has two 10,000 caps (one positive and one negative) already installed which is more than adequate for the amp.

It's NOT a good idea to add the extra caps to the amp. Because of the age you will run the risk of stressing parts in the power supply if you add the circuit. The slight improvement in sound you may get makes it not worth the risk of blowing up components by wiring up the caps wrong or pushing the old parts too hard. We no longer repair the amp so if you wire things up wrong and/or if the power supply fails (which very likely will cause damage to the audio boards) you would be pretty much out of luck.

I suggest simply enjoying the amp as it is!

Larry

amphead · « **Reply #7 on:** 16 Oct 2006, 05:38 am »

I built a 416 about 30 years ago and it still sounds very good.

CE2 · « **Reply #8 on:** 17 Oct 2006, 02:29 pm »

I have seen some for sale on E-bay, do an ebay search for DYNACO, just recently a unit was for sale with the capacitor box, meter front,manual(schematics) it was suppoed to be in great shape. For a 30 year old design and stuff. Things have improved in 30 years.

daveshel · « **Reply #9 on:** 19 Oct 2006, 03:56 am »

I have a 'Black Box 410' that I bought as a kit from Stereo Cost Cutters in 1982, not long after the demise of the original Dynaco. It is a very nice amp, better sounding by far that the ST-120s and ST-150s I have heard. I always figured this was because it was more powerful so it had lots of headroom, but I wonder it it was also a beneficiary of Frank's design enhancements like the ST-416.